@transcender: Please remember that the Kill-a-watt uses a transformerless power supply, and you have to be extremely careful if you're attempting any kind of interface to external electronics. It must be optically isolated, with an independent power supply on both sides of the optoisolators. Not sure if you already know this or not, I just wanted to make sure.

Basically, there is a 5V potential difference between the microcontroller's Vdd and Vss rails, but there is *not* a potential difference of 5 volts between the microcontroller's Vdd rail and mains earth - the 5V rail inside the kill-a-watt will in fact be at about 120VAC or 240VAC relative to mains earth. All the components inside are at the live AC mains potential relative to mains earth.

So if you just bring out a digital line - I2C or serial or whatever it is - from inside the Kill-a-Watt's microcontroller and connect it to another external microcontroller with a conventional power supply, that external microcontroller will see 120 VAC on that line, relative to its own DC ground. Which is a Bad Thing.

The products at Adafruit are great and tutorials very helpful. One such tutorial is the one for Tweet-A-Watt - It seems that P3 has changed their on-board chip, once again :|, to LW2902 instead of the LM2902N as mentioned on the tutorial. Here are some pictures below. Is there a way to get this chip working as there may be a difference in the pin config. For some reason I cant seem to find any spec sheets or rough schematic sheets for this chip to identify the pins on it. Could you help?

Thanks riro424 for sharing the link for the spec sheet. I really hoped there'd be one for the LW2902 as well. TI's website has no sign of that anywhere.

Does it matter that the Kill-a-watt has the LW2902 instead of the LM2902N chip. I could give it a shot with the on-board LW2902 but if I did without being sure that it was similar to LM2902N, I could potentially fry $20 (price for KAW :( ) - Is there an alternative way to establish their similarity?

Lols @ "SW of El Paso" but at this point, I'm not sure where North is :shock: It would really be helpful if this way :arrow: Is pin 1 is closest to R4, R7, R20 or R18?

:mrgreen:note: blackend and underlined alphabet is just to make sure that there are no typos in the part number.

I have the same board as shaheerulasar and I've soldered lines from pins 1, 7, 8, and 14 of the LM2902 (or LW2902?) though I've only gotten 2.3 volts from each one, even with a load. Does anyone know if this is what I'm supposed to read, or perhaps where I could find the voltage or current?

zaqsaw wrote:I have the same board as shaheerulasar and I've soldered lines from pins 1, 7, 8, and 14 of the LM2902 (or LW2902?) though I've only gotten 2.3 volts from each one, even with a load. Does anyone know if this is what I'm supposed to read, or perhaps where I could find the voltage or current?

zaqsaw wrote:I have the same board as shaheerulasar and I've soldered lines from pins 1, 7, 8, and 14 of the LM2902 (or LW2902?) though I've only gotten 2.3 volts from each one, even with a load. Does anyone know if this is what I'm supposed to read, or perhaps where I could find the voltage or current?

I found I was having the same trouble too. Using at 2012 KAW with a surface mount LM2902. I would see a voltage vary between 2.3 and 2.5V. It wasn't until I removed the XBee from the XBee adapter that that the voltage rose up to 6.0V. Placing the XBee module back on the adapter, it then ran ok, send pulses every two seconds and the Python script on my laptop was receiving the data ok.

If I remove power and the big capacitor discharges too far, then I have to remove the XBee module in order for the cap to charge back up again.

So I believe this must be related to the smaller cap which is supposed to hold the XBee reset line for a few seconds after power up to keep this from happening... but I'm not sure where the issue is. Is it in my assembly technique? Or has the design requirement changed since Adafruit developed this 2009? (I know chances are it's my assembly that is at fault ;)

I had decided to revisit this project and am glad to see people active on this thread (somewhat). The plan was to use the LM2902 chip and as seen in the picture posted earlier by me, would use the leftmost pin on the side of the 'dash' on the chip as Pin # 1. I went ahead and soldered the wires as instructed to pins yellow-->Pin#1, White-->Pin#4, Black-->Pin#11 and Orange-->Pin#14. [Pl. see attachment below - its an illustration of the assumed pin numbers on this illusive LM2902 :o . The EXTRAs are there in case this pin number selection fails; I would then reverse the setup which if need be will document.]

I then proceeded to following these steps to check/update the firmware on the XBee modules since I hadn't touched this project for some time.

The following issue came about:[Advisory:This is a tangential issue but does relate to the Tweet-a-Watt setup because this issue relating to XBee could arise in someone else' setup as it did in mine :) ]

Having followed the above steps, selecting version 10ED. and after doing a "write", one of my XBees is now refusing to respond. There is no blinking green light and X-CTU is complaining about failure to enter command mode for this specific XBee module. This is the message I get:

Failed steps taken to troubleshoot:1. I tried reinstalling the FTDI cable driver from windows2. I uninstalled the windows' version of the driver and downloaded one from FTDI Friends. That did not solve the problem. 3. With the FTDI cable connected and XBee module inserted in to the XBee Adapter that I built using these instructions, I tried to do a reset by connecting the GND and RST pins; it did not resolve the problem - how can I confirm that its been reset..?

Observation:I tried testing connectivity with the second XBee module that comes included in the Tweet-a-watt kit, and it seems to communicates fine with X-CTU. I didnt update its firmware and its at 10EC at the moment.

Could the problem be with the XBee module and loading the latest firmware (10ED) updating it from its prior (10EC version). Please help on a way forward..thank you.

After posting the picture of my killawatt board with the chip, I am noticing that its indeed the LM and not the LW2902. Sorry for the confusion but if you look at my earlier posts, the picture clearly looks like the 'M' is a 'W' when in fact the chip is a LM2902. :shock:

[The most recent picture taken/attached above was taken with a 13 mega pixel cell phone camera. Worthwhile shot I must say :)]